Slow weight gain

Slow weight gain is when your baby doesn't gain weight or grow as quickly as expected. It is also known as 'failure to thrive' or 'faltering growth'.

Although every baby is unique, there are some expectations about how much weight they should gain to grow in a healthy way. If your baby's weight and size don't increase over time, it can affect their:

• development
• brain growth
• general health

All babies have periods when they gain or lose weight. Most babies lose up to 10% of their initial birth weight in their first week. However, the majority then regain their birth weight by 2 weeks of age.

Your baby will have their growth checked regularly at each health check with their doctor or nurse. If your baby is consistently losing weight and not growing at the expected rate for their age and sex, they may have slow weight gain.

How do I measure my baby's growth?

It's relatively easy to measure how your baby is growing. All babies need regular health checks with a health professional. These will help to identify if a baby's growth is slow.

Certain markers are used to track your baby's growth, like their:

• weight
• head circumference
• length

Growth charts are used to note changes in your child's measurements. In Australia, World Health Organization (Opens in new tab) (WHO) growth charts are used to measure children aged between birth and 2 years of age.

On average, most babies will:

• double their birth weight by around 4 months of age
• triple their birth weight by 13 to 15 months of age
• increase their birth length 1.5 times in the first 12 months
• increase their birth head circumference by around 11 cm in 12 months

This may depend on their sex.

There are a few reasons why slow weight gain can happen.

Physical or medical causes

There may be a physical or medical reason which causes your baby not to absorb or process nutrients. This means they are unable to use the food (milk or solids) they're eating to grow.

Common medical conditions causing slow weight gain include:

• allergies to food and milk
• if your baby is premature
• gastro oesophageal reflux disease (GORD)
• conditions that cause vomiting
• conditions that mean your baby needs more energy

Conditions that mean your baby needs more energy include:

• cardiac (heart) problems
• respiratory (breathing) issues
• infections or hormone disorders

Your baby may also have slow weight gain if they have a problem breastfeeding. They may have trouble attaching to your breast. If you are concerned that your baby is not breastfeeding well, you can talk to a lactation consultant. They can give you advice and help make sure your baby gets enough milk.

Environmental causes

Environmental factors can also cause slow weight gain. The most common reason is that your baby isn't being fed the right amount of food to help them grow.

Some common environmental causes for slow weight gain include:

• if your baby is not given regular, nutritious milk or food
• if your baby's cues for hunger are missed
• family homelessness or poverty
• health issues that may affect your ability to provide enough food, like disability, chronic illness or mental health issues

Combination of causes

Sometimes slow weight gain is caused by a combination of medical and environmental factors. Babies can refuse to feed or become fussy feeders because of an undiagnosed and untreated medical condition. Babies may continue to be fussy feeders after they have recovered from being sick.

If your baby was premature or small for gestational age (SGA), they can take longer to gain weight after birth and 'catch-up' with babies of the same age.

What if there's no obvious cause for slow weight gain?

It's not always clear what causes a baby to have slow weight gain. Sometimes, no specific cause is found. If so, your doctor or maternal and child health nurse will continue to closely monitor your child's growth and development.

This makes it hard for parents, who feel they're doing everything they can to feed their baby often and help them grow.

Slow weight gain doesn't always mean something is wrong. Some babies may be smaller because of their genetics. If you are shorter or smaller than average, your children are likely to have the same characteristics. Other babies may have a different growth pattern.

It's common for parents to feel stressed and anxious about their baby's growth, especially if they have slow weight gain. If your baby is growing slower than expected and this is causing you to feel stressed or anxious, let your doctor or midwife know. They will be able to refer you to support groups or professionals to help you cope.

If you suspect your baby has slow weight gain, see your doctor or nurse. To diagnose slow weight gain, they can check if your baby:

• is not gaining weight
• is below the third percentile of weight for their age
• has gone down 2 or more major percentile lines over time

Babies diagnosed with slow weight gain would be considered underweight.

You can read about understanding baby growth charts.

Your doctor or midwife may refer your baby to a paediatrician (specialist doctor for children). Sometimes, for babies under 6 months of age, having more breast or formula feeds can provide extra kilojoules (energy) to support their growth.

For babies over 6 months of age, increased solid foods can help with weight gain. If slow weight gain isn't because of how your baby is feeding or an existing disease, your doctor can investigate further.

Regular weight and growth checks are important for babies who have slow weight gain. Check with your child health nurse, doctor or paediatrician how to monitor your baby's growth.

Serious cases of slow weight gain can lead to malnutrition.

If your baby has slow weight gain, they might be more likely to have:

• problems with their thinking and social skills
• problems with movement
• chronic health problems as adults
• problems with learning

Slow weight gain has many different causes and usually can't be predicted. It may not be possible to prevent it.

If you are concerned about your baby's slow weight gain, speak to your child health nurse, doctor or paediatrician.

Call Pregnancy, Birth and Baby to speak to a maternal child health nurse on 1800 882 436 or video call. Available 7am to midnight (AET), 7 days a week.